As part of its Clean Sky 2 initiative, the EU is funding two parallel projects to develop high-speed rotorcraft: the Airbus Helicopters Racer and Leonardo Helicopters Next-Gen Civil Tiltrotor (NGCTR).
Given the range and origin of the suppliers involved in each, as well as the trans-national nature of the airframers, it is slightly crude to split them on purely national lines, but to simplify, the Racer is French-led, while the NGCTR is Italian-driven – more or less.
While Leonardo's effort spans its operations in both Italy and the UK, one of the demonstrator programme's key suppliers is almost entirely rooted in the Mediterranean nation.
Selected in September 2017, the T-Wing consortium is led by the country's CIRA aerospace research institute, located just to the north of Naples. As the name suggests, the group is dedicated to designing and producing the NGCTR's wings.
For NGCTR engineers, wingtip mass poses a heavy strength-versus-lightness challenge
Clean Sky Joint Undertaking
The consortium is heavily weighted towards Italian industry and includes sister firms Magnaghi Aeronautica and Salver – belonging to the same industrial Group and already suppliers of aerodynamic surfaces for the Airbus A220 aircraft; machining expert OMI; and crash-test specialist Step Sud Mare.
The University of Naples Federico II will also supply expertise in experimental dynamics. However, there are interests from outside of the country too: German engineering consultancy IBK Innovation will provide loads and aeroelasticity validation capabilities.
BIG BREAK
But programme chief Luigi Di Palma considers T-Wing a huge opportunity for Italian industry; even developing a conventional commercial aircraft wing is a "novelty" for the country's supply chain, he says. "I don't know when the last aircraft of this category has been developed here."
Initial work began this year with Leonardo to define the requirements for the structure; a preliminary design review is set for 26 November, with a critical design review to follow in 2019, ahead of wing assembly in 2020 and first flight in 2023.
Di Palma says that the 12m (39ft)-span wings will be made out of regular epoxy carbonfibre, with some unconventional features to enable additional fuel to be carried within the structure and integrated components to reduce time and cost.
Core elements of the design focus on ensuring crashworthiness – notably around minimising the risk of fire – and allowing external access to components within the wing, such as the drive shaft, as well as simplifying installation.
To satisfy the latter challenge, T-Wing is erring away from the more "classical" approach of using a series of access panels.
"In this case we are performing some trade-offs with respect to completely removable solutions," says Marika Belardo, chief engineer on the programme.
Because of the novel nature of the wing, Di Palma says that in order to reduce the programme risk, the partners will trial their manufacturing capability "to understand the feasibility of the solution".
That effort has already begun, in part to test the ability of consortium members to use laminates of a greater thickness than they are used to.
"It is very important for us to test the manufacturability of these components and check if there are some processes viable today for final manufacturing of the wing," he adds.
Although regular carbonfibre will be used for the majority of the wing, not least to "minimise programme risk", special consideration will be given to the area around the wingtip-mounted nacelles, where operating temperatures are higher.
"Also consider the design of the tiltrotor – it has a big mass at the [wing]tip. The challenge is to develop a suitable configuration that is stiff enough to handle that mass but is also light enough to fly."
COMPLEX TASK
Although the original contract with Leonardo was dedicated to the wing itself, that has since expanded to also incorporate the control surfaces, creating an additional area of complexity.
The NGCTR will have two control surfaces on each wing: a typical flaperon to provide additional lift and control, alongside a "morphing surface" more specific to the vehicle. This is employed during vertical take-offs where it is rotated through 89° to reduce the airflow from the prop-rotors that is impeded by the wing, thus cutting the power requirement. As the tiltrotor transitions to airplane mode, as it is known, the surface then returns back to a horizontal position explains Antonio Pagano, the chief engineer for this part of the programme.
Leonardo will build on lessons learned from long-running AW609 tiltrotor development
Leonardo Helicopters
While the wingspan is broadly the same as Leonardo's in-development AW609 tiltrotor, the chord is roughly doubled to 1.9m
The structure will be in two parts, partly to simplify any repair process and also to ease manufacturing: making a 12m-long structure would require a much bigger autoclave than the consortium possesses, says Di Palma.
Minimising any inherent aeroelastic instability such as flutter, rather than countering it with the control surfaces, has also been a prime consideration of the project.
"It means that at the moment we have a structure that is free from flutter but we have to analyse other aeroelastic phenomena. We are working on that for the PDR," says Di Palma.
Aside from the addition of the control surfaces to T-Wing's work package, a scope extension under the Clean Sky 2 programme has also seen the consortium gain a number of other responsibilities.
These will include windtunnel testing of the wing to understand the behaviour of the aerofoil, while T-Wing will also study different configurations for the fuel storage system, ideally avoiding the use of bladder-style tanks.
In addition, the University of Naples and CIRA are to conduct a study into the internal and external noise characteristics of tiltrotors using an instrumented AW609 aircraft. The results will be used to improve the design's noise signature.
"It is the first stage of a complex noise optimisation process," says Di Palma.
Although the NGCTR is solely a technology demonstrator effort and can only be taken to technology readiness level 6, Di Palma believes the consortium will be well placed to take advantage should Leonardo eventually launch serial production of an aircraft derived from the effort.
"It is a chance for the future," he says.
Source: FlightGlobal.com
